1. Field of the Invention
The present invention relates to a secondary battery and, more particularly, to a secondary battery that is structured to improve a seal effect between a cap assembly and a can to prevent electrolyte from leaking out of the battery while providing safety and reliability to the battery.
2. Description of the Prior Art
Generally, secondary batteries are compact in size and rechargeable, while providing a large capacity. Well known as secondary batteries are a Nickel metal hydride battery, a Lithium(Li) battery, and a Li-ion battery.
Particularly, the Li-ion battery uses lithium metal oxide as a positive active material and carbon or a carbon compound as a negative active material. Lithium salt dissolved in an organic solvent is used as the electrolyte via which the lithium ions move between positive and negative electrodes. Charging and discharging operations are realized while the lithium ions are moved between positive and negative electrodes.
FIG. 4 shows a conventional Li-ion battery.
A roll electrode assembly 2 is inserted into a can 4 filled with electrolyte, the roll electrode assembly 2 consisting of positive and negative electrodes and a separator disposed between the positive and negative electrodes. Mounted on an upper end of the can 4 is a cap assembly 6.
The cap assembly 6 is insulated from the can 4 by an intermediate gasket 8. That is, the upper end of the can 4 is crimped on an outer periphery of the cap assembly 6 with the gasket 8 interposed therebetween.
The cap assembly 6 comprises a safety plate 14 provided with a safety groove, a current control member 12 disposed on the safety plate 14, and a cap cover 10 disposed on the current control member 12. Attached under the safety valve 14 is a circuit breaker 18 with an insulator 16 disposed therebetween. The circuit breaker 18 is welded on a positive tab 20 so that it is coupled to a positive electrode of the electrode assembly 2.
In the conventional Li-ion battery structured as in the above, to enhance a seal effect between the cap assembly 6 and the can 4, tar 22 is deposited between the gasket 8 and the cap assembly 6. However, because of a chemical reaction between the electrolyte and the tar 22, the tar 22 may melt, deteriorating the seal effect.